The present invention relates to soil science and hydrology and more particularly to the measurement of soil properties.
Plants require an adequate supply of soluble nutrients to grow well. Also, land reclamation and leachate management require the build-up of dissolved salts and pollutants over large areas to be monitored. In both applications, the solute concentration and water content in soil are the two primary control factors. Indeed, solute concentrations and water content in media such as soil, sand and soil-less media can measure and control many soil conditions, such as irrigation and fertilization conditions, surface runoff, erosion and salinity.
Regarding proper fertilization, the lack of nutrients and overfertilization can both cause problems. It is the concentration of the plant available nutrients dissolved in water, rather than the measurement of total nutrients, that is the pertinent concentration, e.g., to determine if fertilization is required (nutrient level too low) or if fertilization should be stopped (nutrient level too high).
Regarding salinity, salinity refers to the presence of major dissolved inorganic solutes or nutritive salts in aqueous samples. The inorganic solutes or nutritive salts include, for example, Mg+, Ca2+, K+, Cl—, SO42−, HCO3−, and CO32−. Salinity is the total concentration of such salts. For agricultural applications, it is imperative to ensure that the salinity level is not too high. For example, most crops are tolerant of a salinity range between 0 and 100 mS/m and intolerant of a salinity range between above 400 mS/m. Irrigation water should also be checked to ensure that its salinity is not too high.
The conductivity of water in soil (referred to herein as pore water) indicates the presence or lack of the above-listed nutritive salts. Pore water conductivity has been measured in the past by suctioning the pore water from the soil or by creating a saturated soil paste and measuring the conductivity of such paste. Those methods are time consuming and error prone. Another technique for estimating pore conductivity is a dielectric technique known as time domain reflectometry (“TDR”). The TDR technique is relatively expensive and difficult to handle for example in a greenhouse in which multiple samples of different pottings of soil need to be taken.
A need therefore exists to provide a soil analysis measurement and control device that can handle each of the above applications, which is relatively easy to use and transport, which can take relatively quick readings, which can take multiple readings in series to monitor different soil portions, and which is relatively inexpensive and rugged.